Process and apparatus for providing image brightness over a wide range of discharge repetition rates

ABSTRACT

This disclosure deals with a novel voltage-multiplying power supply process ad apparatus particularly adapted, through the use of a reactive voltage drop within the supply circuit, to produce substantially constant power in repetitive discharges of stored energy, irrespective of the variation in repetition rate of the discharges, within wide limits.

United States Patent 1191 1111 3,735,238 Miller 1451 May 22, 1973 [54]PROCESS AND APPARATUS FOR FOREIGN PATENTS OR APPLICATIONS PROVIDINGIMAGE BRIGHTNESS OVER A WIDE RANGE OF DISCHARGE REPETITION RATES 367,7852/1932 Great Britain ..321/l5 OTHER PUBLICATIONS [75] Inventor: Cha l EMi]l A ,M IBM Technical Disclosure Bulletin, Self-Regulated Pulse PowerSupply, Vol. 9, No. 11, April, 196, p. [73] Ass1gnee: General RadioCompany, Concord, 1,666

Mass- Electronics, Multiplier Phototube," July 8, 1960 Vol. 22 Filed:Sept. 17, 1971 33 28 51 PP 181,547 Primary Examiner-William M. Shoop,Jr.

AttorneyRines & Rines [52] US. Cl. ..321/15, 315/241 P, 315/241 S TR![51] Int. Cl. ..H02m 7/00 [57] ABS CT [58] Field of Search ..315/200,227, 241 P, This disclosure deals with a novel voltage-multiplying315/241 s, 272, 273, 352, 353; 321/15 Power pp y prwess ad apparatusParticularly adapted, through the use of a reactive voltage drop [56]References Cited within the supply circuit, to produce substantiallyconstant power in repetitive discharges of stored energy, UNITED STATESPATENTS irrespective of the variation in repetition rate of thedischarges, within wide limits. 3,412,311 11/1968 Siedband ..32l/15 X3,329,247 7/ 1967 J aeschke ..321/ 15 X 3 Claims, 5 Drawing Figures -gc4 2 R 3 P H C 2 c1 2 E F R1 Patented May 22, 1973 2 Sheets-Sheet 1F/Gi! H T v mo 5o S150 finiaw IY C LOAD CURRENT FIG. 20

FIG. 2b

Patented May 22; 1973 2 Sheets-Sheet 2 FLASH RATE (FLASHES- PER-SECOND)I; M u

6 m 2 Gtii 5.20.

FIG. 3

PRIOR ART DISCHARGE CAPACITORE PROCESS AND APPARATUS FOR PROVIDING IMAGEBRIGHTNESS OVER A WIDE RANGE OF DISCHARGE REPETITION RATES The presentinvention relates to processes and apparatus for supplying energydischarges to a load, such as a flashtube and the like, that is to berepetitively energized by voltage supplied by a voltage-multiplyingpower supply.

The invention will be particularly described in connection with itspreferred application to repetitively discharged loads, such asflashtubes, discharge gaps and similar devices, as for such applicationsas stroboscopy and the like, though it is to be understood that thebasic features thereof are equally applicable to the supplying ofvoltage to loads from voltage-multiplying power supplies of thischaracter in other applications, as well.

Turning, however, to the application to stroboscopy and the like, theart is replete with all kinds of resonant charging power supply circuitsand other voltagemultiplying circuits, such as doublers, quadruplers,etc., which have been adapted to deliver voltage to flashtube dischargecircuits and similar loads for the production of high energy flashes oflight and other energy.

Voltage multiplier power supplies are particularly well suited for usein small portable equipments, having the advantages that, in practice,they are typically smaller, lighter weight and less expensive thanequivalent transformer-operated supplies. Among such systerns are thosedescribed in, for example, US. letters Pat. Nos. 2,342,257; 2,478,901;2,965,807; 3,115,594; 3,267,328; 3,286,128; 3,340,426; 3,354,379;3,463,992; 3,513,376; and RE 24,823. Unfortunately, none of thesetechniques sufficiently accommodates for the desirable variation inenergy from the power supply discharged into the flash lamp or similarload when the rate of repetition of the charging and discharging orflashing varies over wide limits. While attempts have been made to tryto render more uniform the energy per flash over a wide range ofrepetition rates, these efforts have not proven adequately satisfactoryand they have been accompanied by several disadvantages hereinafterexplained.

The subjective image brightness to an observer using the stroboscope isproportional to flash lamp power, with the power in the lamp being alsoproportional to the energy per flash times the flash repetition rate. Aflash lamp has a maximum power limit, however, that cannot be exceededwithout damage. It is thus common practice to design a stroboscopecircuit to produce the greatest possible light output commensurate withthe limitations dictated by the components, allowable heat rise, etc.

In wide-range stroboscope circuits of this character, for example, thecharging resistor or resistance in the flash lamp anode circuit is ofsuch value that the storage or discharge capacitor normally rechargescompletely between flashes, producing a constant illumination eachflash. Maximum power to the lamp and maximum subjective image brightnessthus occurs at or near the maximum flash repetition rate, and thesubjective image brightness decreases approximately in proportion to thedecrease in flash repetition rate. Following each flash, the dischargecapacitor is recharged to the power supply output voltage by currentflowing through the charging resistor, with a consequent dissipation ofpower by the resistor in the form of heat equal to the power in the lampat the particular flash repetition rate.

The value of the charging resistor may be adjusted with relation to thedischarge capacitor to increase the time required to charge thecapacitor with respect to the shortest interflash period. By suitableselection of voltage, resistance and capacitance values, the capacitordoes not recharge completely at higher flash repetition rates. This cancompensate somewhat for the loss of light at lower flash rates byproviding an increasing anode voltage at decreasing frequencies; butthis is subject to the principal disadvantage that such resistivecompensation causes heat to be lost in the resistor in excess of thepower dissipated in the lamp at high repetition rates. This isespecially disadvantageous in small instruments or in instrumentsemploying plastic enclosures the integrity of which might be jeopardizedat elevated temperatures.

Other suggestions have involved range-changing circuits that introducedifferent-size capacitors; but these are not only relatively complicatedand costly, but they disadvantageously involve an exponential factor asthe flash rate is varied or have practical effectiveness only over anarrow maximum-minimum flash rate ratio for each range if relativelyconstant subjective image brightness is desired.

An object of the present invention, accordingly, is to provide a new andimproved process and apparatus for supplying voltage to a load, such asa repetitively discharged flash lamp and the like, that shall not besubject to the above-described disadvantages, but that, to the contrary,enables substantially constant power automatically to be produced in theload irrespective of variation in the discharge repetition rate overwide ranges thereof and without excess heat losses or complexrange-changing circuits.

In summary, this result is attained by providing a substantially purereactive voltage drop within the power supply circuit itself thatenables a substantially linear variation of stored voltage with currentproduced thereby through the load as the result of discharge, thusenabling substantially constant power to be produced in the load for awide variation in the discharge repetition rate.

A further object of the invention is to provide a novelvoltage-multiplier power supply apparatus and process of more generalapplicability, as well.

Other and further objects will be described hereinafter and will be moreparticularly pointed out in connection with the appended claims.

The invention will now be described with reference to the accompanyingdrawing,

FIG. 1 of which is a schematic circuit diagram illustrating a preferredform of the invention, operating in accordance with the process thereof,and illustratively shown adapted to the triggering of flashtubes orother lamps, as in the stroboscope and similar applications:

FIG. 2 (a) is an equivalent circuit diagram of the circuit of FIG. 1,designed in accordance with the invention;

FIG. 2 (b) is a graph illustrating the phenomenon underlying theoperation of the invention and plotting load current along the abscissa.

FIG. 3 is a graph illustrating the performance of the circuits of FIG. 1and hereinafter described FIG. 4, plotting the lamp and chargingresistor power for the preferred form of the invention of FIG. 1, andthe resistor power in the conventional prior art stroboscope circuit ofFIG. 4; and

FIG. 4 is an equivalent circuit diagram of such a typical prior artconventional stroboscope circuit.

Referring to FIG. 1, a quadrupler power supply (at first blush ofconventional configuration) is shown comprising a source 1 of, forexample, alternatingcurrent input voltage, (or any similar input voltagesource), connected to enable the storing or charging of direct-currentvoltage in capacitors C1, C2, C3 and C4, with the aid of rectifiers R,,R R and R, In this circuit, the rectifiers are connected in series andin closed charging loops containing capacitors C and C, also connectedin series. The rectifier R, is disposed in a first closed charging andstoring loop circuit with the capacitor C, and rectifiers R and R aresimilarly connected in a loop containing capacitor C Capacitors C, and Care connected in series with rectifiers R, R and R and the input fromthe source 1, with the point of series connection 6 between thecapacitors C, and C being connected between the rectifiers R, and R Thepoint P of series connection of the capacitors C and C, is similarlyconnected between the rectifiers R 2 and R Through this construction,the familiar quadrupling effect is produced such that at the outputterminals 3 and 5, high voltage is available and stored in capacitor 12through charging resistor 11, for discharge between the anode and thecathode of a flash lamp or similar load 2 that is to be repetitivelytriggered by, for example, a variable repetition rate trigger circuit 4,in conventional fashion, as disclosed in the above-reference patents.

For many years, it has been considered essential, as taught in theliterature, to use relatively large values of storage capacitors C,through C, in order to minimize output voltage regulation with loadcurrent fluctuations. In addition, the filtering of ripple due to thealternating current source voltage has consistently been considered inthe art as necessary through the use of such large capacitors.

In accordance with a discovery underlying the present invention,however, it has been found that by reducing at least one of theappropriate capacitors to a very small capacitance value, far less thanthe values required for voltage regulation before-discussed, an entirelynew phenomenon and operation occurs that, in addition, solves a problemunderlying the present invention. Specifically, as the capacitor C ismade of a very low value, a substantially pure capacitivereactance-limited effect is provided which produces a reactive voltagedrop within the supply circuit giving rise to a substantially linear,not exponential, variation of the ultimate output voltage charge andstored at the output terminals 3 and with discharge current producedvthrough the load 2 in response to triggering at 4, as more particularlyshown in the graph of FIG. 2 (b).

This phenomenon can be more readily understood by reference to theequivalent Thevenin circuit shown in FIG. 2 (a), wherein V representsthe no-load supply voltage, R represents the Thevenin resistance, and Rrepresents a variable resistance load. The load voltage of such acircuit varies in the linear manner shown by the regulation curve 8 ofFIG. 2 (b), with the slope determined by the value of R The advantage ofthis circuit is that the magnitudes of the V and R may be set over wideranges by varying the number of stages of voltage multiplication and thevalues of the storage capacitors, respectively.

While this unconventional small intermediate series reactance capacitorC will give rise to large ripple voltages across itself as the loadcurrent increases, the large values of capacitance C, and C, in theoutput have been found to serve most adequately to minimize such ripple,as seen by the load, and thus reduce the attendant undesirableshort-term fluctuation of light output. Image brightness compensation ofthe flashes produced by the lamp 2 with variation in dischargerepetition rate over wide ranges is effected by the resulting reactivedropping of the supply voltage, substantially eliminating any resistiveexcess heat dissipation in the charging resistor 11, as shown in theflat curve 9 of FIG. 3, and, in view of the linear characteristics ofFIG. 2 (b), resulting in a substantially constant power supplied to thelamp and image brightness over a wide flash lamp rate or repetitionrange. Since the ripple on the flash lamp voltage is maintained low overthe range of output voltage variation, satisfactory uniformflash-to-flash lighting output has been thus obtained. In addition, alow ripple content low voltage may be provided to power other circuits7, as at point 6 in F IG. 1, by proper placement of the reactivedropping capacitor C as shown. Curve 10 in FIG. 3, on the other hand,illustrates the power which would be dissipated as heat in the chargingresistor 13 of the corresponding conventional stroboscope circuit ofFIG. 4, demonstrating the marked efficacy of the invention.

In a successful circuit of this character, the values of capacitors C,and C, were set at the large regulation value of 24 p. and the capacitorC, was set to almost 3 times that value at 69 11.. The reactancelimiting capacitor C, was adjusted to the relatively very small value of1.3 u, producing an output voltage V, of approximately 650 to 350 voltsover the normal range of flash rate (0 to 60 flashes per second). Thecircuit had a Thevenin resistance of approximately 14.7 kilohms andproduced approximately 8 watts maximum output.

The above technique is also obviously applicable to othervoltage-multiplying circuits where this type of output regulation isdesired, and further modifications are thus considered to fall withinthe spirit and scope fo the invention as defined in the appended claims.

What is claimed is:

l. A process for supplying voltage to a load such as a flashtube and thelike that is to be repetitively discharged by voltage periodicallycharged and stored in a voltage-multiplying power supply, thatcomprises, applying alternating-current voltage to a plurality ofinterconnected capacitor storage circuits each comprising closedcharging and storing loops containing separate voltage-multiplyingcapacitors and rectifier elements with certain of the loops sharingcommon rectifier elements to enable voltage multiplication, triggeringthe discharge of the stored voltage developed across the storagecircuits to discharge the same through the load, controlling saidtriggering to effect the same repetitively, each time following thesubstantially complete voltage charging and storing in the plurality ofstorage circuits, varying the repetition rate of said charging andstoring, and adjusting the value of at least one of thevoltage-multiplying capacitors to a value very small compared with thelarge voltage-regulating capacitance value of other of thevoltage-multiplying capacitors to eliminate substantial resistivedissipation with variation of repetition rate and to provide asubstantially linear variation of stored voltage across the storagecircuits with current produced thereby through the load, when triggered,in order to produce substantially constant power in the loadirrespective of the variation in the said repetition rate.

2. Apparatus for supplying voltage to a load such as a flashtube and thelike that is to be repetitively discharged, having, in combination,voltage-multiplying circuit means containing a plurality ofvoltagemultiplying storage capacitors connected with a plurality ofrectifiers in closed loops sharing certain of the rectifiers and havingan output circuit, means for connecting a load to be repetitivelyenergized from the voltage periodically stored in the output circuit,means for varying the rate of repetition of such storing and energizingof the load, and means comprising a voltage multiplying capacitoradjusted to a value very small compared with the value of said storagecapacitors and connected in the voltage-multiplying circuit therewith toprovide substantially constant power in the load irrespective ofvariation in said repetition rate.

3. Apparatus as claimed in claim 2 and in which the rectifiers andcapacitors are adjusted so that ripple of the output voltage due to theinput alternating current voltage is negligible for any level of outputvoltage supplied to the load and determined by the flash repetition rateand consequent load current irrespective of the variation of the flashrepetition rate.

1. A process for supplying voltage to a load such as a flashtube and thelike that is to be repetitively discharged by voltage periodicallycharged and stored in a voltage-multiplying power supply, thatcomprises, applying alternating-current voltage to a plurality ofinterconnected capacitor storage circuits each comprising closedcharging and storing loops containing separate voltage-multiplyingcapacitors and rectifier elements with certain of the loops sharingcommon rectifier elements to enable voltage multiplication, triggeringthe discharge of the stored voltage developed across the storagecircuits to discharge the same through the load, controlling saidtriggering to effect the same repetitively, each time following thesubstantially complete voltage charging and storing in the plurality ofstorage circuits, varying the repetition rate of said charging andstoring, and adjusting the value of at least one of thevoltagemultiplying capacitors to a value very small compared with thelarge voltage-regulating capacitance value of other of thevoltage-multiplying capacitors to eliminate substantial resistivedissipation with variation of repetition rate and to provide asubstantially linear variation of stored voltage across the storagecircuits with current produced thereby through the load, when triggered,in order to produce substantially constant power in the loadirrespective of the variation in the said repetition rate.
 2. Apparatusfor supplying voltage to a load such as a flashtube and the like that isto be repetitively discharged, having, in combination,voltage-multiplying circuit means containing a plurality ofvoltage-multiplying storage capacitors connected with a plurality ofrectifiers in closed loops sharing certain of the rectifiers and havingan output circuit, means for connecting a load to be repetitivelyenergized from the voltage periodically stored in the output circuit,means for varying the rate of repetition of such storing and energizingof the load, and means comprising a voltage multiplying capacitoradjusted to a value very small compared with the value of said storagecapacitors and connected in the voltage-multiplying circuit therewith toprovide substantially constant power in the load irrespective ofvariation in said repetition rate.
 3. Apparatus as claimed in claim 2and in which the rectifiers and capacitors are adjusted so that rippleof the output voltage due to the input alternating current voltage isnegligible for any level of output voltage supplied to the load anddetermined by the flash repetition rate and consequent load currentirrespective of the variation of the flash repetition rate.